Sleepy Neurons Lead to Mistakes

In sleep-deprived rats random brain cells take "naps" while the animal is awake. This leads to performance problems.

If you’ve ever felt like your brain is not quite "online" some days, and you have more errors in judgment, brain blips, or make more mistakes than usual, sleepy neurons may be to blame. A new study finds that when animals are sleep-deprived but awake, their brain cells may randomly take "catnaps," which leads to more lapses in judgment than well-rested animals.

"Such tired neurons in an awake brain may be responsible for the attention lapses, poor judgment, mistake-proneness and irritability that we experience when we haven't had enough sleep, yet don’t feel particularly sleepy."

In the new study, the researchers measured the brain activity of sleep-deprived rats. Certain brain areas were analyzed specifically, and overall sleep vs. wake states were also confirmed with EEG. The rats were kept awake not by any bizarre or cruel methods, but with environmental stimulation: they were given new toys, like balls, boxes, and tubes to crawl through, and interesting nesting materials that smelled like other rats.

The longer the rats were awake, the more likely were certain subsets of neurons to turn off, or "go offline" briefly. When neurons snoozed in this way, their electrical patterns matched those of neurons in slow-wave sleep, even though the rest of the brain was awake. But there was no apparent rhyme or reasons to which neurons switched off when. Lead author Giulio Tononi says that "[s]trikingly, in the sleep-deprived brain, subsets of neurons go offline in one cortex area but not in another — or even in one part of an area and not in another."

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When brain cells in the motor cortex "napped," the animals were more likely to make mistakes when reaching for food pellets. And the more sleep-deprived the rats were, the more likely they were to make mistakes.

Does this relate to humans, too? Absolutely, says Tononi: "Such tired neurons in an awake brain may be responsible for the attention lapses, poor judgment, mistake-proneness and irritability that we experience when we haven't had enough sleep, yet don’t feel particularly sleepy."

While other animals, like dolphins, use "local sleep" as an adaptive mechanism (half of the brain sleeps while the other half stays awake), it’s not clear what the function of the phenomenon described here is. For example, sleepy brain cells may be trying to recover from the overload brought on by sleep deprivation. Future studies will need to hash out the details of exactly why neurons take cat naps, and whether the same mechanisms are going on in humans.

The study was carried out by researchers at the University of Wisconsin-Madison, and published in the April 28, 2011 issue of Nature.